In U.S. Pat. No. 5,789,768 issued to Biing-Jye Lee et al., and assigned to the same assignee as the present application, a structure, as shown in FIG. 1, of a light emitting diode (LED) having high brightness is disclosed. In this structure, a semiconductor substrate 12 of n-type GaAs is formed on an n-type back electrode 10, and a distributed Bragg reflector (DBR) layer 30 is formed on the semiconductor substrate 12. AlGaInP or AlGaAs is preferably used in forming this DBR layer 30. A stacked structure 14 is formed on the DBR layer 30. The stacked structure 14 includes a bottom n-type cladding layer of AlGaInP 140, an active layer of AlGaInP 142, and a top p-type cladding layer of AlGaInP 144. A p-type window layer 16 is formed on the top cladding layer 144. Transparent material, such as GaP, GaAsP, GaInP or AlGaAs is preferably used to form the window layer 16. A p-type contact layer 17 is formed on the window layer 16. GaAsP, GaP, GaInP, or GaAs is preferably used to form the contact layer 17. A transparent conductive layer 19 is formed on the contact layer 17, extends into the central through hole of the contact layer 17, and contacts with the window layer 16. Tin oxide, indium oxide, or indium tin oxide (ITO) is preferably used to form the conductive layer 19. A p-type front electrode 20 is formed on the conductive layer 19.
This prior light emitting diode is characterized in that an ohmic contact is formed between the conductive layer 19 and the contact layer 16, and the interface between the conductive layer 19 and the window layer 17 results in a Shottky barrier. Therefore, the current from the front electrode 20 spreads out in the conductive layer 19, passes through the ohmic contact without passing through the Shottky barrier, and flows into the active layer 142 wherein it meets the current from the back electrode 10 and achieve the light emitting effect.
Although the current from the front electrode can be controlled to pass through the ohmic contact without passing through the Shottky barrier in this prior light emitting diode, part of the current will flow toward the location directly below the front electrode 20 when passing through the window layer 16. This part of the current flows into the active layer 142 at the location directly below the electrode 20, meets the current from the back electrode 10 there, and thereby results in light emitting effect. All of those who are skilled in the art know that the light emitted from the active layer at the location directly below the electrode 20 will be blocked by the electrode 20 and this will result in a low light emitting efficiency.
In the construction of the second embodiment disclosed in U.S. Pat. No. 5,153,889 issued to Hideto Sugawara et al., a current inhibiting layer is provided between a window layer and an upper clad layer to control the current distribution. However, the disadvantage of this prior light emitting diode lies in that it has to be formed in two epitaxial processes. More specifically, after forming the current inhibiting layer on the upper clad layer, the undesired portion of the current inhibiting layer has to be removed. After this, the second epitaxial process for forming the window layer can be carried out. The costs of equipment, manufacturing time, and yielding good products incurred by two epitaxial processes are much higher than those by a single epitaxial process.